The present invention relates to a protocol conversion system between a subscriber terminal and a communication network, and/or between communication networks.
The X.25 protocol has been used for high speed data communication. However, X.25 protocol is not compatible with conventional telephone network, PBX, and ISDN (integrated service digital network). Therefore, the X.32 protocol has been developed for those purposes. However, the X.32 protocol needs specific equipment, and conventional X.25 equipment is not compatible with X.32 communication.
FIG. 9 shows a prior data communication network. In the figure, the X.25 apparatus C may communicate with another X.25 apparatus D through the data communication network 400. The data communication network 400 has the X.32 correspondence portion 400A for the communication with an X.32 apparatus. X.32 apparatus B which is coupled with a telephone network, ISDN or PBX 300 may communicate with another X.32 apparatus which is coupled with the telephone network 300, and also communicate with a X.25 apparatus C or D through the X.32 correspondence portion 400A and the data communication network 400.
However, a X.25 apparatus A cannot couple to the telephone network 300.
Further, in the X.25 protocol system, terminal equipment is coupled with a communication network through a subscriber's circuit for Packet Switched Public Data Network, and therefore, no data communication is possible by using a public telephone network, a PBX, and an ISDN circuit.
Further, if the protocol of the first network differs from that of the second network, the address system and the parameters of the first protocol differ from those of the second protocol, and no communication is possible between the first protocol and the second protocol.
Accordingly, it is preferable that an X.25 protocol apparatus may access to a data communication network through a public telephone network, PBX, and/or ISDN. And, it is desirable that X.25 protocol equipment may communicate with X.32 protocol equipment, and/or X.25 equipment may communicate with other X.25 equipment through a public telephone network. The address system and the parameters of a protocol must be converted for coupling different protocols.